Study Identifies Invasive Species in Long Island Sound

For over 30 years, Ellen Thomas, Harold T. Stearns Professor of Integrative Sciences, emerita, and Johan Varekamp, Harold T. Stearns Professor of Earth Science, emeritus, have been researching microorganisms in the Long Island Sound and the impacts of climate change in the region. The researchers recently discovered an invasive species by analyzing new and archival mud samples with novel microscope technology and genetics research, as detailed in a paper they co-authored in Science Advances.

Thomas, Varekamp, and first author Eleanor Goetz, a Ph.D. student from Yale University, found the microscopic species, Ammonia confertitesta, in samples from the Long Island Sound. The microorganism is native to the Jiozhou Bay in China and was deposited in the Sound as early as 1820, the researchers said. They even tried to locate the very ship that could’ve brought the first traces of these organisms to Long Island in the late 1700s.

“This is the true liberal arts approach to doing science, where you try to actually track the very ship that could have brought the organism here,” said Varekamp, also Smith Curator of Mineralogy and Petrology of the Joe Webb Peoples Museum. “…putting the human and commercial history between China and the U.S. in context—something that scientists rarely do.”

This finding challenges a long-held assumption that the smallest organisms in an ecosystem are generally native to the areas they inhabit. The first rare specimens of Ammonia confertitesta didn’t take hold in the region for decades. Thomas and Varekamp found the population spike in the 1970s, taking over as the dominant microorganism in the western part of Long Island Sound, close to New York. This follows a global pattern of increases in aquatic invasive species in the mid-to-late 20th century, in accordance with an uptick in globalized trade and container shipping activity.

The researchers said it is widely accepted that invasive aquatic species like bacteria, animals, and viruses are carried in the ballast water of cargo ships—water stored on ships to provide stability during a voyage. Ballast water is taken on in one region before being discharged in coastal waters of another region, and the organisms in the ballast waters can pose a threat to the ecosystem where they are dumped.

The researchers speculated that in the 1990s the boom in this species spreading eastward in Long Island Sound was possibly due to environmental factors, such as deoxygenation, water temperature increase, metal pollution, and declining water salinity. But such environmental factors were present already in the 1850s, according to their earlier research, long before Ammonia confertitesta spread out into Long Island Sound. They initially suggested in their earlier work that the microorganisms could be an invasive species, and the current study with genetic data confirmed this.

The Long Island Sound is an example of an estuarine habitat—a partially enclosed coastal body of water with a mix of freshwater and saltwater—that provides critical space for breeding and nursery, filtering of polluted runoff water, and a buffer-zone from coastal erosion. Estuarine ecosystems are highly susceptible to disturbances from climate change, urbanization, and industrialization, the authors noted. The introduction of non-native species like Ammonia confertitesta can further compound the disruption of these ecosystems, the researchers said.

The paper also reaffirms the value of proper storage of research samples, which, in this case, have been collected at considerable cost. These samples and data are available for future use, when new technologies become available.

“Observation of small organisms with skeletons that are preserved in mud, in dated core samples, provide important records on the history of species invasions,” said Thomas, also Smith Curator of Paleontology of the Joe Webb Peoples Museum. “The abundance and relative importance of invasive species in coastal ecosystems with severe anthropogenic disturbance thus can be tracked in a quantitative way worldwide.”